I've begun digging into PubSubHubbub, the real-time RSS update protocol created by Brad Fitzpatrick and Brett Slatkin of Google and Martin Atkins of Six Apart. I was under the impression that it's harder for RSS publishers to use than the RSSCloud Interface, but that isn't the case. The specification is simple and precisely written, adopting conventions like RFC 2119 that make a spec considerably easier to understand, and it communicates using basic HTTP requests.

I wrote the software that runs the Drudge Retort, so I decided to add Pubbub support to it this morning to see how it works. (I'm tripping over the name "PubSubHubbub" like crazy, both when I write and speak, so I'm giving the protocol a nickname.) Pubbub delegates all the work required for update notification to a server called a hub. Google offers a hub at http://pubsubhubbub.appspot.com/ that's free for use by all feed publishers, so I'm relying on it.

First, I added a link element to the Retort's RSS feed that identifies the feed's update hub:

<atom:link rel="hub" href="http://pubsubhubbub.appspot.com" />

Because this element comes from the Atom namespace, I had to make sure it was declared in the feed's top-level RSS element:

The bold portion is the Atom declaration. I already was using an Atom element in the feed, so I didn't need to change this.

When a new story is posted on the Retort, the Pubbub hub must be notified that a change has occured. This is handled by sending a ping to the hub with the URL of one or more feeds that have been updated.

I've written an open source Weblog Pinger library in PHP, so I upgraded it to support these pings. A Pubbub ping employs HTTP requests (REST) instead of XML-RPC, the protocol used by Weblogs.Com and similar services. I wrote a new function, ping_rest(), that can send a ping to any Pubbub server.

By the time I was done, I'd spent an hour on the code and a few hours testing it out. So now when I post a new item on the Retort, Google's Pubbub server sends the full text of the item to all readers that support the protocol. This is faster and simpler than RSSCloud, which tells readers to request the feed again.

To give you an idea of how fast Pubbub can be, when I posted a new story on the Retort, it showed up 20 seconds later on FeedBurner, one of the first RSS services to support the protocol.